1. Technical Field of the Invention
The present invention relates to engine starters which include a motor that generates torque for starting an engine, a main electromagnetic switch for selectively opening and closing an electric circuit for supplying electric power from a battery to the motor, and an auxiliary electromagnetic switch for selectively switching the electric circuit between a high-resistance path and a low-resistance path.
2. Description of the Related Art
Conventionally, a starter for starting an internal combustion engine generally includes a motor that generates torque for starting the engine and an electromagnetic switch that selectively opens and closes an electric circuit for supplying electric power from a battery to the motor.
However, when activation of the motor is started, in other words, when the electric circuit is closed by the electromagnetic switch, a large current, which is generally called inrush current, flows from the battery to the motor. Consequently, the terminal voltage of the battery drops rapidly and thereby may cause an instantaneous power failure to occur. Here, the term instantaneous power failure denotes a phenomenon in which electric devices other than the motor which are powered by the battery instantaneously stop operating due to the rapid drop in the terminal voltage of the battery.
Moreover, due to the large current, the motor will generate a high torque, thereby increasing the impact force between a pinion of the starter and a ring gear of the engine during the establishment of engagement therebetween. Consequently, wear of the pinion and the ring gear will increase, thereby lowering durability of the starter and the engine. In addition, a high level of noise will be generated during the establishment of engagement between the pinion and the ring gear.
To solve the above problems, there is disclosed, for example in Japanese Patent Application Publications No. 2009-224315 and No. 2009-167967, a technique of selectively switching the electric circuit for supplying electric power from the battery to the motor between a high-resistance path and a low-resistance path.
Specifically, according to the technique, a resistor is inserted in the electric circuit to form both the high-resistance and low-resistance paths. Along the high-resistance path, electric power is supplied from the battery to the motor through the resistor. On the other hand, along the low-resistance path, electric power is supplied from the battery to the motor bypassing (i.e., without passing through) the resistor. Further, an auxiliary electromagnetic switch is employed to switch the electric circuit between the high-resistance and low-resistance paths.
More specifically, when activation of the motor is started, the auxiliary electromagnetic switch switches the electric circuit to the high-resistance path, causing only a limited current, which is limited by the resistor, to be supplied from the battery to the motor. Consequently, the terminal voltage of the battery is prevented from rapidly dropping. As a result, it is possible to prevent an instantaneous power failure from occurring, thereby ensuring normal operation of the other electric devices powered by the battery. Moreover, with the limited current, the motor will generate only a limited torque, thereby reducing the impact force between the pinion of the starter and the ring gear of the engine when establishing engagement therebetween. As a result, wear of the pinion and the ring gear will be suppressed, thereby improving durability of the starter and the engine. In addition, it is possible to suppress the level of noise generated during the establishment of engagement between the pinion and the ring gear.
As soon as the pinion and the ring gear are fully engaged, the auxiliary electromagnetic switch switches the electric circuit to the low-resistance path, thereby allowing the full voltage of the battery to be applied to the motor. Consequently, with the full voltage applied, the motor will rotate at a high speed to start the engine.
In addition, in recent years, the use of engine automatic stop/restart systems (also called idle stop systems) has been increasing in order to reduce global warming. For a starter used in an engine automatic stop/restart system, the number of times the starter operates to start or restart the engine is considerably increased; thus, it is necessary for the starter to have high durability. Accordingly, the above-described technique is particularly effective when applied to starters used in engine automatic stop/restart systems.
Moreover, according to the disclosure of Japanese Patent Application Publications No. 2009-224315 and No. 2009-167967, the auxiliary electromagnetic switch is fixed to a housing of the starter via a bracket.
More specifically, the housing has a switch-mounting portion to which the main electromagnetic switch is fixed by means of two bolts. The bracket has first and second end portions. The first end portion has an end surface to which the auxiliary electromagnetic switch is joined by, for example, welding. The second end portion has two through-holes formed therein. The second end portion is interposed between the switch-mounting portion of the housing and the main electromagnetic switch and fixed therebetween by fastening the two bolts which respectively pass through the through-holes of the second end portion.
However, with the above fixing structure, the auxiliary electromagnetic switch is fixed to the bracket and the bracket is fixed to both the housing of the starter and the main electromagnetic switch. In other words, it is necessary to fix the bracket along with the auxiliary electromagnetic switch not only to the housing of the starter but also to the main electromagnetic switch. Consequently, flexibility in fixing the auxiliary electromagnetic switch in the starter is lowered, thus also lowering flexibility in mounting the starter with respect to the engine.